Membrane oxidative damage induced by ionizing radiation detected by diphenylhexatriene fluorescence lifetime distributions.

The sensitivity of the fluorescence lifetime of 1,6-diphenyl- 1,3,5-hexatriene (DPH) to the dielectric constant of its environment has been used to detect oxidative damage to phospholipid membranes induced by ionizing radiation. The DPH fluorescence decay in phospholipid vesicles is described well by a continuous distribution of lifetime values, reflecting the various DPH depths in the bilayer and related to the gradient of the dielectric constant. Ionizing radiation oxidizes unsaturated acyl residues of phospholipids, altering the dielectric constant across the bilayer, sharpening the distribution of DPH lifetimes and increasing the centre of the distribution. Ionizing radiation doses between 22 and 110 Gy were used, and were effective only in the presence of oxygen. A model based on the formation of packing defects in the bilayer describes the phenomenon.